Crystal plating apparatus

ABSTRACT

A crystal plating device and method thereof in which a crystal to be plated and thereby set at a desired frequency is placed in an external removable holder or slug for insertion into a chamber of a plating device. The device is connected to a vacuum pump which is activated after the slug is loaded. Spring loaded filament posts carry a filament of precious metal such as gold or silver. The crystal is oscillated at a predetermined frequency prior to the filament being energized to evaporate or atomize the metal which plates the crystal and sets it frequency identical to that of the oscillator. 
     The slug is externally loaded and can carry different size crystals. It is fitted with masks to accurately direct the deposit of the metal upon either or both sides of the crystal. After plating the slug is easily removed from the plating device.

This is a division of application Ser. No. 034,780 filed Apr. 30, 1979,now U.S. Pat. No. 4,236,487.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to plating of materials and more particularly tovacuum plating of crystals.

2. Description of the Prior Art

Crystals can be made to oscillate at a natural frequency, or byappropriate and selective plating can be manufactured to oscillate at adesired exact frequency. With the increased importance of electronics inour daily lives, crystals have gained widespread use in the circuitryfor communications, and clocks and the like.

Depending upon how exacting the frequency is to be set the crystal mayfirst be base plated, on one or both sides before being final coated,again on one or both sides. In the more accurate frequency work it isrecommended to coat both sides of the crystal to avoid "spurs" which isthe occurrence of random peaks caused by aberrations of unknown origin.

In the frequency range of the present invention the fundamental andovertones thereof have been tested up to 450 Mega Hertz and above, andhave tested out with great accuracy of 2 ppm up to frequencies of atleast 150 Mega Hertz.

In the prior art it was conventional practice to use a fixture carryingthe crystal to be final plated and enclosed by a bell jar. Prior toplating the jar was evacuated. In this method the frequency accuracy waslimited to 90 Mega Hertz, and even at this value test equipment showedthe need to compensate to bring the frequency to within accepted levels.

Heretofore vacuum crystal plating was done in a bell jar in which thecrystal had to be internally loaded with tweezers into a special holderwithin the bell jar. The entire bell jar then had to be evacuated,including the special holder for the crystal. The vacuum was then drawnthru a narrow opening and was not as absolute as desired. The relativesize of the vacuum equipment, the complexly shaped items that werewithin the vacuum chamber provided multiple surfaces to which air orother contaminants could adhere. The presence of these contaminants,together with the difficulties in removing them results in deficienciesin the plating process and resultant deficiencies in the productproduced.

Additionally, the internal loading of the crystals within the bell jaris relatively time consuming and therefore expensive. Also, because ofthe size and shape of the vacuum equipment, much of the noble metalvaporized in the plating process never reaches the crystals to becoated. Instead, it is randomly deposited on the walls of the bell jaror surfaces of the crystal holder. Therefore, the plating process islengthened and much of the noble metal used in the plating process isineffectively used.

The randomly deposited noble metal is recovered by cleaning the surfaceswithin the bell jar. However, because of the complexly shaped andrelatively large surfaces the cleaning process is not as quick or easyas desired.

SUMMARY OF THE INVENTION

To overcome these problems, the present invention sets forth apparatusand method for plating crystals in a crystal plating device and methodthereof in which a crystal to be plated and thereby set at a desiredfrequency is placed in an external removable holder or slug forinsertion into a chamber of a plating device. The device is connected toa vacuum pump which is activated after the slug is loaded. Spring loadedfilament posts carry a filament from which is hung a wire of preciousmetal such as gold or silver. The crystal is oscillated by means of acontrollable external oscillator circuit while the filament is beingenergized to vaporize or atomize the precious metal. The particles ofvaporized precious metal adhere to and plate the crystal, therebysetting the frequency of the crystal within a predetermined desiredrange.

The slug is externally loaded and can carry different size crystals. Itis fitted with masks to accurately direct the deposit of the metal uponeither or both sides of the crystal. After plating, the slug is easilyremoved from the plating device, and the plated crystal then removedfrom the slug.

Accordingly, it is an object of the present invention to provide acrystal plating device which reduces the vacuum pumping time; it isanother object of the present invention to provide a crystal platingdevice which has a relatively small vacuum chamber.

Yet another object of the present invention is to provide a crystalplating device which enables alignment of the crystal to be plated to bemade externally of the vacuum chamber.

A further object of the present invention is to provide a crystalplating device which does not require extensive alignment of the crystalwithin the vacuum chamber.

It is an additional object of the present invention to provide a crystalplating device which has relatively easy to clean internal surfaceswithin the vacuum chamber.

Another object of the present invention is to provide a crystal platingdevice which minimizes the amount of time required for loading of thechamber.

Still another object of the present invention is to provide a crystalplating device which facilitates effective use of the noble metal usedin the plating process.

It is yet another object of the present invention to provide a crystalplating device which minimizes waste of the noble metal used in theplating process.

Another object of the present invention is to provide a crystal platingdevice which enables easy and rapid replace of filaments used forvaporizing the plating materials.

An additional object of the present invention is to provide a crystalplating device which is relatively reliable in use.

It is a further object of the present invention to provide a crystalplating device which can plate crystals of different size.

It is an additional object of the present invention to provide a crystalplating device which does not require modifications of the chamber tovary the size of the crystal being plated in the chamber.

Yet another object of the present invention is to provide a crystalplating device which can base plate and/or final coat crystalsinterchangably and/or as one sequence.

An additional object of the present is to provide a crystal platingdevice which can adjust he point at which plating occurs on threeperpendicular axes.

It is another object of the present invention to provide a crystalplating device which can plate crystals on either or both sides.

It is also an object of the present invention to provide a method forplating crystals which minimizes the time required for plating thecrystals.

Still another object of the present invention is to provide a method forplating crystals which minimizes the number of operations which must beperformed within the vacuum chamber.

It is yet another object of the present invention to provide a methodfor plating crystals which enables alignment of the crystal intended forplating to be performed outside of the plating chamber.

Still another object of the present invention is to provide a method forplating crystals which enables alignment in three perpendicular axes ofthe crystal intended for plating.

It is an additional object of the present invention to provide a methodfor plating crystals which enables alignment of the crystal simply andwithout need for special tools.

A further object of the present invention is to provide a method forplating crystals which can plate crystals of different size withoutinterrupting or disrupting the plating process.

It is an additional object of the present invention to provide a methodfor plating crystals which can plate either side or both sides of thecrystal simultaneously.

Another object of the present invention is to provide a method forplating crystals which allow accurate adjustment and positioning on thecrystal of the material to be deposited.

Other objects and advantages will be apparent from the followingdescription of the invention; and the novel features will beparticularly pointed out hereinafter in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a side perspective view of the crystal device of the presentinvention.

FIG. 2 is a side elevational view of the crystal device of the presentinvention.

FIG. 3 is a top plan view of the crystal device taken along line 3--3 ofFIG. 2.

FIG. 4 is an upturned side view of the crystal device taken along line4--4 of FIG. 3.

FIG. 5 is a bottom plan view of the crystal device taken along line 5--5of FIG. 2.

FIG. 6 is a side elevational view, partly in section, of the springbiased filament post.

FIG. 7 is a top plan view of the crystal holder or slug in the openposition as taken along line 7--7 of FIG. 8.

FIG. 8 is a side elevational view taken along line 8--8 of FIG. 7.

FIG. 9 is a front elevational view taken along line 9--9 of FIG. 7.

FIG. 9A is a front elevational view of FIG. 9 wherein the pivoted maskholders are shown in raised posistion.

FIG. 10 is a top plan view of one of the final calibration masks.

FIG. 11 is a side elevational view of the mask of FIG. 10.

FIG. 12 is a schematic representation of the crystal oscillating circuitand the filament circuit showing the filaments mounted across adjacentpairs of filament posts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention as illustrated in FIGS. 1-12 teaches an improvedcrystal device and method thereof in which a crystal 20 is to be plated.In one embodiment the plating which brings the crystal to its desiredfrequency, commonly termed final plating is shown, and it is understoodthat the crystal blank can be base coated as desired in any suitablemanner well known in the prior art. Another embodiment is shown in whichthe crystal can be base plated.

With reference to FIGS. 1, 2, 3, 9 and 12, the crystal 20 is plugconnected within a crystal holder or slug 22 which when in its closedposition is inserted into a slot 24 of a base 26 in communication with achamber 28 in which is disposed two pairs of filament posts 30, one oneach side of the crystal 20 and across which is mounted a filament 60 onwhich is hung a gold or silver wire 32. The base 26 is connected at theopen bottom of the chamber 28 via the manifold in dotted lines, to asuitable vacuum pump (not shown) which may have a control valve. The top33 of the base 26 has an annular "O" ring 34 which will seal against thetop cover 36. The cover 36 has a rim which fits about the circular top33 to snugly seal the top upon the vacuum within the chamber 28. Thevacuum pumping time is reduced due to up to 80% less volume than priorart chambers and also the use of a wide mouth opening at the bottom ofthe chamber 28.

Two separate and independent electrical circuits are run within the base26. The first circuit is made by a pair of shielded wires 38 having acommon shield 40 which is grounded to the base 26 at the wire feedthrough retainer plate 42 connected to the base 26 by a fastener 44.Each wire 38, one of which is illustrated in FIG. 5 extends insulatinglythrough a metal tube fitted within a counterbore 46 within the base andsealed by and "o"-ring 48. The inner end of each wire 38 connects to alead pin 50 which extends partially into the slot 24 near its bottom.

A contact pin 52 is disposed in each end of an insulated block 54 of theslug. Each pin 52 contacts a receptacle tube 55 extending upward throughthe insulating block 54. A lead 58 from the crystal is fitted into thepassage in each receptacle tube. Each crystal lead 58 is connected to aspring loaded receptacle 56 connected by conductive epoxy to one side ofthe crystal 20. The other lead 58 is connected to the other side of thecrystal and is received in a second receptacle tube 55 which iscontacted within the block 54 by a second pin 52 extending externallyfrom the opposite side of the block 54.

Once the crystal 20 is mounted within the receptacle tubes 55, 55 viaits leads 58, 58 a series circuit will be formed running from one wire38, to pin 50, pin 52, receptacle tube 55, lead 58, spring receptacle56, crystal 20 and then out the other side wherein the components appearin reverse order.

The wires 38, 38 are connected to a frequency oscillator (not shown)which incorporates the crystal 20. The oscillator with the crystal isconnected to a frequency counter which monitors the changes in frequencyas the plating process proceeds. It will be understood that anyconventional oscillation circuit and oscillator can be used in order toachieve the improvements of the present invention, and therefore nospecific details thereof have been set forth herein.

The power circuit is connected to a suitable power supply (not shown)wherein conductive filaments 60 are attached as shown in FIGS. 3 and 12across adjacent filament posts 30, as more fully described hereinafterand the posts 30 are connected in series, with the last (4th) post 30grounded to the base 26 to complete the power circuit. Upon energizingthe power circuit a current of approximately 30 amps and 1 volt willpass through the circuit and the filaments 60 so as to vaporize thesilver (or gold) wire 32 which are positioned on the filaments 60 whichbeing adjacent to the crystal 20 will be directed through the masks 62mounted in the holder 22 to be deposited upon one or the other of thesides of the crystal 20 so as to plate the crystal. Because the currentis high and the voltage low the only things that gets hot are thefilaments 60, and the wires of silver hanging on the filaments. Thefilament posts 30 of which three of the four are insulated from the base26 are of much larger mass than that of the filaments 60, and will actas heat sinks so as to greatly reduce cycle time.

The crystal holder assembly or slug 22 is illustrated in FIGS. 7, 8 and9 wherein the insulated block 54 has insert guides 62 connected alongits length on opposite sides thereof. The lower edge 64 is leveled atthe external bottom edge to aid insertion of the slug within the baseslot 24, and has corner cut outs 66 at each upper corner edges, as isshown in FIG. 9A. Hinge pins 68 extend parallel to the insulator block54 from the vertical face of the cut outs 66 to pivotally receive hingesupports 70 which are square rod which are fitted with slotted maskholders 72 which are adjustably connected to the supports 70 by screws74 to slide within the mounting slots 76 between a retracted positionfor small size crystals 20 and an extended position for larger sizecrystals 20.

The holder has a longitudinal shoulder 78 which ends the lower step 80formed to permit the mask holders 72 to be raised vertically withoutinterfering with the insulated block 54, as illustrated by the dottedline representation of FIG. 8. Aligned inwardly facing flanges 82 act asstops to prevent overswinging of the mask holders 72 and contacting ofthe crystal 20 or abutment of the screws 74. An aperture 84 circularlysloped with a longitudinal bore formed on one side as shown in FIG. 7 toreceive a retaining spring 86 which holds a circular mask 88 therein.The mask 88 has a flared down keyhole nozzle 90 which will direct theevaporated silver toward the crystal 20.

An alternate mask 92 is shown in FIGS. 10 and 11 wherein a taperednozzle 94 is eccentrically formed to permit adjustment thereof to alignthe mask nozzle 94 relative the crystal 20. It will be understood thatthe mask 88 can be used for base plating, while the mask 92 can be usedfor final plating.

The crystal 20 will be connected within the receptacle tube 55 to placethe crystal 20 in the oscillating circuit. The hinged mask holder 72will be in the open position shown by the solid lines of FIGS. 8 and 7and 9. Thereafter the holders 72 will be raised vertically to present anarrow profile shown by the dotted lines of FIG. 8 and in FIG. 9A forinsertion within the slots 24 of the base 26 as shown in FIGS. 3 and 5.The contact pins 52 will electrically engage the lead pins 50 so thatwhen the oscillator is activated the circuit will be completed and thecrystal will oscillate to enable the plating process to procede.

The base 26 has a circular lower diameter 96 which is reduced to asmaller upper diameter 98 by an annular step back at 100, while the sideadjacent the lead retainer 42 has a slabbed step 102 which extends froma tangent of the upper circle downwardly along a straight wall whichterminates in a narrow horizontal platform 104 that extends to the fulldiameter 96 and extends underneath the leads 38. The slabbed step 102permits the leads 38 to be shortened and thereby keep the capacitance toa very low value thus increasing the accuracy of the oscillator circuitto the crystal 20 and eliminating the need to compensate for thefrequency setting.

The slot 24 is formed in chamber 28 along a line parallel to the slabbedstep 102. Inwardly from the ends of slot 24 and on opposite facing sidesthereof are two pairs of cloverleaf apertures 108, three of which aresized to receive an insulating sleeve 110 which fits about the filamentholders 70 and insulates it from the base 26. The forth filament holder30 is slidingly disposed within a smaller diameter opening to begrounded to the base 26.

The chamber 28 extends top to bottom of the base 26 and includes theclover leaf aperture 108 in communication with the slots 24.

The filament post 30 is part of a filament post assembly 112 whichincludes the insulating sleeve 110 and the filament 60, and andinsulated filament post holder 114 having a horizontal mounting flange116 through which a mounting screw 118 passes to be threadedly receivedin a tapped hole in the base 26 as shown in FIGS. 2, 4, and 5. There isone holder 114 for each pair of posts 30. The inner surface 120 betweenthe posts 30 is hogged out of the chamber 28 in a contour to aid vacuumexcavation.

The holder 114 has two bottom recesses 122 illustrated is FIG. 4 andvertical holes 124 central thereto through which threaded members 126extend to receive a pair of nuts 128 and a connecting strip 130 whichextends between the three posts 30 which have the insulated sleeves 110and is held upon the members 126 by a third nut 128 as shown in FIG. 5.

The first of the posts 30 is connected to an internal power supply lead133 which is in turn connected to an external power supply lead 132 thatextends through a metal sleeve 134 and is insulated therefrom, while thesleeve is sealed at its inner end by an "O" ring 136 to prevent an airleak into the vacuum chamber 28. A retainer 138 having a bifurcated endpositions the wire 132 within the sleeve 134 and sealingly holds thesleeve 134 within the feed through bore of the base 26, with theretainer 138 being held in position by a threaded fastener 140. (SeeFIG. 2.)

The filament post 30 illustrated in FIG. 6 with a tapped hole throughwhich the threaded member 126 and will be screwed down to rest upon aninternal nut 129 which sets the posts 30 height. The body 142 is hollowwith an inturned annular flange 144 at its upper end through which afastener button 146 extends to trap the fastener 148 within the body142. The fastener has an annular radial slot 150 below which thefastener has a reduced diameter so that the spring retainer 152 toengage the upper end of a coil spring 154 the lower end of which restsupon the bottom of the body 142 and is disposed about the threadedmember 126.

The spring 144 will normally urge the fastener 148 upwardly so that theslot 150 is raised above a pair of diametrically opposite body slots156. The tension of the spring 154 can be set by adjusting the body 142upon the member 126 with internal 129. The height of the body 142 can beadjustably set by raising or lowering the external nuts 128 and thenbring the body 142 to rest thereupon.

The insulated sleeve 110 has a cut out 158 which uncovers the body slots156 of adjacent facing filament posts 30 as shown in FIG. 3 so thatwhenever a filament 60 is to be connected the operator will depress thebutton 146 to align the slot 150 of the fastener 148 with the body slot156 so that the end of a filament 60 can be inserted therein. Releasingthe button 146 allows the spring 154 to force the fastener 148 upwardlyto entrap the filament 60 end within the fastener 148 and securely wedgeit between the now non-aligned slots 150 and 156. Thus the delicatesilver wire filaments 60 is easily and securely fastened between theadjacent pairs of posts 30. The height of the post 30 has been set tocorrespond to the crystal 20 size and the opening 94 of the mask 92.

The power circuit shown in FIGS. 3, 5 and 12 shows the power lead 132which is connected to a suitable source of power making a circuit frompost 30 (or strip 130) to filament 60, to post 30, to strip 130, to post30, to filament 60, to uninsulated post 30 which is grounded to the base26 so as to complete the circuit. When the power source is energized,after the slug 54 is assembled within the base 26, and the vacuumestablished in the chamber 28, the electrical energy will heat thefilaments 60 and cause the silver to be vaporized and the nozzle 94 ofthe mask 92 will direct the silver to be deposited upon the oscillatingcrystal 20 controlled by the oscillating circuit described hereinbefore.

It should be noted that alternative power circuits to the filament headsare also possible. For example, the pairs of filament posts can beconnected in parallel, or can be provided with separate external powersupplies.

SUMMARY OF METHOD AND DISCUSSION OF ADVANTAGES Operation

Prior to performing plating operations, the chamber is thoroughly clean.This is easily accomplished by disconnecting internal power supply lead133, unfastening mounting screws 118 and removing the pairs of filamentposts 30. The chamber can then be easily cleaned by any convenientcleaning implement such as a toothbrush. The individual filament postscan be disassembled down to the main components and similarly cleaned.

After cleaning, the apparatus is reassembled and connected to the powersupply and the oscillator. Filaments are placed within and connectingadjacent filament holders to complete the electrical circuit. A strandof silver or gold (depending on which is desired) is then placed on thefilament on the side of the crystal where plating is desired, or on bothfilaments if plating is desired on both sides.

The chamber is then connected to an appropriate source of vacuum,normally by placing the chamber on top a vacuum manifold so that thevacuum can be drawn from the bottom of the chamber.

A crystal to be plated is mounted in a slug in preparation for plating.Depending on whether base plating or final plating is to be conducted,an appropriate plating mask is placed in the mask holder of the slug.

Wide ranges of crystal size can be accomodated in the chamber by usingcrystal holders which are sized to compensate for the differentdimensions of the crystals and still bring the crystals into properlocation for plating. Any size variation that can't be accomodated bymeans of different size crystal holders or slugs may be accomodated byadjustment of the height of the filament holders.

One or more crystal holders or slugs can be used in the plating process.Preferably several slugs will be used to insure that the vacuum chamberwill not be idle while crystal are being mounted in slugs for plating.

The arms of the slug or crystal holder are placed in the uprightposition bringing the mask into operative association with the face ofcrystal. The masks are manipulated to the position that will deposit thematerial in the desired location on the crystal.

By rotating the mask, it is possible to adjust the horizontal and/orvertical position of the eccentrically positioned orifice in the maskwith respect to the face of the crystal. Also, the mask may bepositioned vertically within the mask holder and will be held inposition by means of spring 86. Additionally, spring 86 will hold theposition of the mask in the plane perpendicular to the face of thecrystal, so that this position can be set by merely pushing the maskwith the fingers towards or away from the face of the crystal. Theposition of the mask perpendicular to the plane of the crystal face isimportant to control and minimize the dispersion of the atomized orvaporized metal that has passed throught the orifice prior to adheringto the face of the crystal.

The crystal holder or slug is then placed in slot 24 of chamber 28 sothat the contact pin 52 of the slug will make electrical contact withthe lead pin 50 from the oscillator lead.

The cover of the chamber is then put in place and seals automatically asthe vacuum is drawn from the bottom of the container.

Power is provided to oscillator to which the crystal in the slug isconnected and incorporated. The frequency of oscillator is accuratelymeasured by a frequency meter to which the oscillator is connected.Plating of the crystal can be started once the crystal beginsoscillating. Plating is commenced by connecting the power supply to thefilament by an appropriate switch which has not been shown. The heat inthe filament combined with the vacuum in the chamber vaporizes thestrand of silver hanging on the filament. As the vaporization proceeds,particles of the vaporized material are deposited and condensed on theunmasked portion of the crystal. The frequency of the crystal willchange as the build-up of condensed material continues on the crystal.

When the frequency counter indicates that the crystal frequency hasreached the desired value, the power to the filaments is discontinued.Because of the relatively small size of the filaments as compared to thefilament holder, the heat will be rapidly drawn away from the filamentscooling them sufficiently to quickly end vaporization of the platingmaterial.

After plating has been completed the vacuum is released and the slug orcrystal holder is removed and another inserted for the next platingoperation.

The strands of plating material are easily positioned for plating bymerely placing them to hang from the filament. After repeated platingoperations, the filaments themselves will deteriorate. However, the areeasily replaced by merely depressing the fastener button 146 to removethe old filament and replace it with a new filament.

It should be noted that the the interchangeability of masks and/or slugsallows for the plating of different size crystals in the same chamberwithout modifying the chamber in any way to accommodate the differentsize crystals.

Also, because the different masks can be used interchangeably, it isconvenient to separately perform either base coating and/or finalcalibration coating procedures in the same chamber. Further, if desired,because of the superior qualities of this apparatus, it is possible toconduct both the base and final calibration procedures during a singleoperation in the apparatus. This single or "one step" procedure is usedwhen the final product does not require intermediate processing stepsoften employed to insure compliance with more stringent crystalperformance specifications.

From the above discussion it is clear that there are many advantages ofthe present apparatus. For example, the vacuum chamber 28 is ofrelatively small volume and is relatively uncomplicated in shape.Therefore, it can be evacuated quickly and offers relatively few shapesor areas in which pockets of gas tend to adhere or resist evacuation. Byusing removable crystal holders or slugs to mount the crystal, allcrystal adjustment can be made at places remote from the vacuum chamberwhere there is adequate working room and where the process of adjustingthe crystal in the holder will not interfere with the plating operation.After the plating has produced a build-up of the plating material on thewalls of the chamber, the unused plating material can easily berecaptured by the ease of cleaning the plating chamber.

The relative small volume of the vacuum chamber combined with the use ofthe slugs to hold and adjust the crystals prior to plating insures thatthe actual cycle time for performing the plating in each of the crystalsis relatively short. Additionally, almost all of the valuable platingmaterial can be recaptured without difficulty by the simple cleaningprocess mentioned previously.

It will be understood that the various changes in the details,materials, arrangements of parts and operating conditions which havebeen herein described and illustrated in order to explain the nature ofthe invention, may be made by those skilled in the art, within theprinciples and scope of the invention.

What is claimed is:
 1. A crystal holder for plating crystalscomprising:(a) an insulating base; (b) a pair of receptacle tubesextending upward from said insulating base to receive a pair of leadsfrom the crystal and make electronical contact therewith, and to mount acrystal on said insulating base; (c) a pair of opposing hinge platespivotally connected to said insulating base; (d) a mask holder disposedon each of said hinge plates; (e) an apertured mask disposed in eachhinge plate; and (f) said opposed hinge plates coacting to bring saidapertured masks into operative position with a crystal mounted on saidinsulating base.
 2. The combination claimed in claim 1 furthercomprising a spring disposed in each of said hinge plates to secure theposition of said apertured mask disposed in said hinge plate.